This invention relates generally to the manufacture of semiconductor devices and more specifically to a handling device that thermally conditions devices and presents them to a test system.
In the manufacture of integrated circuit chips, the chips are generally tested at least once. The test results are used in various ways. They can be used to separate good chips from faulty chips. They can also be used to grade parts. For example, chips are usually rated by the maximum speed at which they can operate or by the amount of the data they can store, with the chips having a higher speed or larger memories being sold at higher prices. Often, variations in the chip manufacturing process result in some chips operating at a higher speed or having more usable memory. The test results allow the parts that have greater capabilities to be graded for sale at a higher price. In some cases, defects on chips can be repaired using laser repair stations or similar equipment. Another way that test results might be used in the manufacture of chips is to guide the repair of chips.
Usually, automatic test equipment is used to run the tests. A handling device is used to present the chips to the automatic test system in an automated fashion. A handling device that handles packaged parts is usually referred to as a xe2x80x9chandler.xe2x80x9d To fully test chips, tests are often run at multiple temperatures over the rated operating range of the chip. For example, many chips are tested over a range that spans from xe2x88x9255 deg C. to +155 deg C. The handler, in addition to moving the chips to and from a test station, often heats or cools the parts to the desired test temperature.
The main drawback of present test handler thermal systems, which are mainly convection based, are the long slew times (20 to 60 minutes) and long soak times ( greater than 2 minutes). xe2x80x9cSlew timexe2x80x9d refers to the length of time it takes for the handler to reach the desired operating temperature. xe2x80x9cSoak timexe2x80x9d refers to the amount of time a chip must be in the handler until it reaches the desired temperature for a test.
A short slew time is important in being able to quickly recover from jams or machine failures, especially during cold testing when the machine must often be reheated to remove frost and condensation. In addition, the slew time and the soak time affect the package changeover timexe2x80x94the time it takes to reconfigure a machine to test a new type of device. The slew time plays a role in that when a package changeover is needed the handler must be brought back to an ambient-level temperature, the hardware and software configuration changes made, and then brought to the desired test temperature. Once the machine reaches temperature, the soak time plays a role in that it defines the time it takes for the first device to reach the test site, if the system is not mechanically limited in speed. Finally, in the case where a new lot of devices is loaded, the soak time plays the dominating role and defines the time it takes for the first device to be tested, if the system is not mechanically limited in speed. The slew time and soak time become even more dominant in describing the overall effectiveness or efficiency of a machine, because the frequency of new lots and changeovers has constantly been increasing.
In addition many convection based thermal systems end up rather large and have trouble with tight temperature control of devices, particularly in the case of high parallel test. Conduction-based thermal systems have in the past been considered for use in test applications. However, they do not provide a means to achieve a high thermal slew rate design that meets the test temperature range and tolerance requirements (xe2x88x9255 deg C. to 155 deg C. and xcx9cxc2x12 deg C.). The greatest use of conduction based thermal systems in test today is in probe applications (wafer test), where a temperature-controlled chuck (thermal chuck) provides a means to support, transport, align, temperature control and test the ICs on a wafer.
Thermal chucks are available commercially such as from Thermonics Incorporated of Santa Clara Calif. and Temptronic Corporation of Newton Mass. These wafer chucks have limited performance capability over the complete hot-and-cold test temperature range. Specifically, their slew-rate performance is limited because they use a closed-loop mechanical refrigeration system needed for clean-room operation. Their slew-rate performance is also limited because the thermal mass of the thermal chuck is too large.
Closed loop refrigeration systems generally can not provide a fast enough and great enough cooling and heating source to achieve the desired short ramp rates (xcx9c5 minutes) over the complete xe2x88x9255 deg C. to 155 deg C. temperature range. In addition, these thermal chucks are all single-zone thermal systems, where heating and cooling of the chuck is regulated by feedback from one temperature sensor. In probe applications however, slew rates are not as important because of the much longer time it takes to test a wafer than it takes to test a group of packaged devices; a wafer can hold hundreds of ICs. In addition, all ICs are processed on a very limited number of different wafers, differing only in diameter e.g. 200 mm, 300 mm. Therefore, the number of different chuck designs is very limited, and the only changeover typically is that necessary to change the test interface, probe interface components, or software/test program. On a final note, the soak time is generally much faster for a wafer than it is for a packaged device because of the extremely high surface finish and flatness of a wafer and high thermal conductivity of silicon compared with the properties of traditional packaged devices (e.g. ceramic and xe2x80x9cplasticxe2x80x9d packaged parts). Given this and the low influence of the soak time, probers are not built with thermal conditioning buffer capacity.
Conduction-based thermal systems in package test (handler applications) have been used, but these were mainly for active temperature control of high-power devices under test, and therefore require feedback of the device or the device die (junction) temperature as in the prior patents by Jones (U.S. Pat. No. 5,420,521) and by Tustaniwskyj (U.S. Pat. No. 5,821,505). This functionality of active temperature control based on device power dissipation is not required for the large majority of ICs which are relatively low-power devices (less than about 10 W), therefore this adds unnecessary cost and control complexity (control-feedback system required and intended for each device). Furthermore, typically only the high-end microprocessor devices have built-in temperature sensors, which could be used for temperature control purposes during test (U.S. Pat. No. 5,821,505). An external control element such as in Jones (U.S. Pat. No. 5,420,521), requires that the sensor align with and contact each device under test. Given the vast nature of device types, achieving alignment of the temperature sensors with each device type/package type is difficult, costly, and time consuming. Finally, these systems as described in Jones (U.S. Pat. No. 5,420,521), Tustaniwskyj (U.S. Pat. No. 5,821,505), and Tustaniwskyj (U.S. Pat. No. 5,844,208) require a clamping action to sandwich the device between the conduction system and the electrical test socket to achieve the necessary pressure between the device and the conduction system. In automation equipment, it is most often necessary and preferred to handle (pick up) and hold devices down using vacuum. The patents by Tustaniwskyj (U.S. Pat. No. 5,821,505) and Tustaniwskyj (U.S. Pat. No. 5,844,208) clearly state that additional mass changes the intention, performance, and nature of their invention.
The conduction-based design by Micro Component Technology Inc. of St. Paul, Minn. in U.S. Pat. No. 5,966,940 requires the use of thermoelectric elements. A xe2x80x9cthermo-electric elementxe2x80x9d refers to a device that will generate heat when a electricity is applied in one direction and will cool when electricity is applied in the opposite direction. These provide a means for some local hot and cold temperature tuning but are relatively expensive, fragile, difficult to assembly in large numbers (necessary for greater cooling/heating capacity), require excessive electricity and greater control-system complexity, and have a limited heating/cooling capacity. Thermo-electric elements also require a heat sink during cold operation. In the prior art this is overcome by implementing a closed-loop heating/refrigeration system, which ends up providing the bulk temperature control. Closed loop refrigeration systems generally can not achieve the desired 5 minute ramp rate over the complete xe2x88x9255 deg C. to 155 deg C. temperature range.
Early handlers operated on single chips that slid on rails through the handler. As devices got smaller, some handlers began to use boats that carried single parts or a small number of parts. Some handlers used trays to carry many loose devices and to present multiple devices to a test site in parallel. An example of a tray type handler is shown in U.S. Pat. No. 6,024,526.
More recently, it has been suggested that a handler should operate on chips before physically severing/separating the devices from the common lead frame or circuit-board substrate. Leaded devices are assembled and packaged in finite groups on a lead frame. Typically grid array devices are manufactured on a flexible or rigid substrate (circuit board) called a strip. Lead frames and strips together are often referred to generically as panels. FIG. 15 illustrates a plurality of IC devices 115 in a lead frame 116. In manufacturing chips, a lead frame or substrate is provided. Some portion of the lead frame or strip is used for the electrical leads and connections, and other portions are used to mechanically hold the devices in place. In the manufacturing process, there are equipment and processes to cut the electrical connections and the mechanical connections. To test devices still attached to a lead frame or a strip, only the electrical connections are severed.
While handlers have been suggested to operated on chips in strips, it would be desirable to have an improved strip type handler.
With the foregoing background in mind, it is an object of the invention to provide a handler that provides fast slew rate and fast soak times.
It is also an object to provide a handler that can operate on devices in lead frames or strips.
The foregoing and other objects are achieved in a handler having a plate with multiple temperature control zones in intimate contact with chips being tested.
In one embodiment, the plate includes vacuum ports to draw chips in lead frames or strips against the plate.
In another embodiment, the plate has multiple heating or cooling zones.